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[clang codegen] Use IR "align" attribute for static array arguments. 

Without the "align" attribute, marking the argument dereferenceable is
basically useless.  See also D80166.

Fixes https://bugs.llvm.org/show_bug.cgi?id=46876 .

Differential Revision: https://reviews.llvm.org/D84992
This commit is contained in:
Eli Friedman 2020-07-30 17:32:39 -07:00
parent 6b1f9f2bd4
commit 673dbe1b5e
2 changed files with 17 additions and 9 deletions
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16
clang/lib/CodeGen/CGCall.cpp
View File

@ -2520,6 +2520,9 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
// bytes). // bytes).
if (ArrTy->getSizeModifier() == ArrayType::Static) { if (ArrTy->getSizeModifier() == ArrayType::Static) {
QualType ETy = ArrTy->getElementType(); QualType ETy = ArrTy->getElementType();
llvm::Align Alignment =
CGM.getNaturalTypeAlignment(ETy).getAsAlign();
AI->addAttrs(llvm::AttrBuilder().addAlignmentAttr(Alignment));
uint64_t ArrSize = ArrTy->getSize().getZExtValue(); uint64_t ArrSize = ArrTy->getSize().getZExtValue();
if (!ETy->isIncompleteType() && ETy->isConstantSizeType() && if (!ETy->isIncompleteType() && ETy->isConstantSizeType() &&
ArrSize) { ArrSize) {
@ -2539,10 +2542,15 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
// For C99 VLAs with the static keyword, we don't know the size so // For C99 VLAs with the static keyword, we don't know the size so
// we can't use the dereferenceable attribute, but in addrspace(0) // we can't use the dereferenceable attribute, but in addrspace(0)
// we know that it must be nonnull. // we know that it must be nonnull.
if (ArrTy->getSizeModifier() == VariableArrayType::Static && if (ArrTy->getSizeModifier() == VariableArrayType::Static) {
!getContext().getTargetAddressSpace(ArrTy->getElementType()) && QualType ETy = ArrTy->getElementType();
!CGM.getCodeGenOpts().NullPointerIsValid) llvm::Align Alignment =
AI->addAttr(llvm::Attribute::NonNull); CGM.getNaturalTypeAlignment(ETy).getAsAlign();
AI->addAttrs(llvm::AttrBuilder().addAlignmentAttr(Alignment));
if (!getContext().getTargetAddressSpace(ETy) &&
!CGM.getCodeGenOpts().NullPointerIsValid)
AI->addAttr(llvm::Attribute::NonNull);
}
} }
// Set `align` attribute if any. // Set `align` attribute if any.

10
clang/test/CodeGen/vla.c
View File

@ -200,13 +200,13 @@ void test7(int a[b(0)]) {
// Make sure we emit dereferenceable or nonnull when the static keyword is // Make sure we emit dereferenceable or nonnull when the static keyword is
// provided. // provided.
void test8(int a[static 3]) { } void test8(int a[static 3]) { }
// CHECK: define void @test8(i32* dereferenceable(12) %a) // CHECK: define void @test8(i32* align 4 dereferenceable(12) %a)
void test9(int n, int a[static n]) { } void test9(int n, int a[static n]) { }
// NULL-INVALID: define void @test9(i32 %n, i32* nonnull %a) // NULL-INVALID: define void @test9(i32 %n, i32* nonnull align 4 %a)
// NULL-VALID: define void @test9(i32 %n, i32* %a) // NULL-VALID: define void @test9(i32 %n, i32* align 4 %a)
// Make sure a zero-sized static array extent is still required to be nonnull. // Make sure a zero-sized static array extent is still required to be nonnull.
void test10(int a[static 0]) {} void test10(int a[static 0]) {}
// NULL-INVALID: define void @test10(i32* nonnull %a) // NULL-INVALID: define void @test10(i32* nonnull align 4 %a)
// NULL-VALID: define void @test10(i32* %a) // NULL-VALID: define void @test10(i32* align 4 %a)